Air bearing sliders have been extensively used in disc drives to appropriately position a transducing head above a rotating disc. The transducing head is typically carried by the slider. Conventionally, head positioning is accomplished by operating an actuator arm with a large-scale actuation motor, such as a voice coil motor (VCM), to radially position the slider over a track on a disc. Typically, disc drive systems include a suspension assembly attached to the actuator arm for supporting and positioning the slider. The suspension assembly includes a load beam attached to the actuator arm and a gimbal disposed at the opposite end of the load beam. A flex circuit material is deposited on the gimbal and the actuator arm. The air bearing slider carrying the transducing head is mounted to the flex circuit material. This type of suspension assembly is used with both magnetic and nonmagnetic discs. The VCM rotates the actuator arm and the suspension assembly to position the transducing head over a desired radial track of the disc.
In order for the disc drive to read and write data from the transducing head, conductive traces are disposed along the flex circuit material of the suspension assembly for the disc drive to electrically communicate with the slider. The traces extend along the gimbal and end at flex on suspension (FOS) bond pads formed adjacent to the slider. The slider has a forward face with bond pads disposed on the forward face such that an electrical connection can be made between the traces and the slider. Typically gold ball bonds are used to provide the connection between the FOS bond pads and the slider bond pads. Difficulties have arisen in prior art systems for attaching the slider to the gimbal, and in particular with respect to aligning the slider bond pads to the FOS bond pads.
Several factors affect slider alignment to the FOS bond pads. These factors include flex circuit material alignment to the gimbal, slider alignment to the gimbal, the dimensional features of the gimbal, slider and flex circuit material, and the method of assembly. Slight variations in each of these combine to form a tolerance stack-up, which is the addition of variations that occur during the assembly of the suspension assembly. A poor suspension assembly design fails when the variations are extreme.
The head gimbal assembly (HGA) product design evolved from a FOS over to a FOS under trace routing with the advent of HGA automation. A FOS over design employs a FOS on the non-disk side of the HGA with flying FOS traces tab bonded to the slider bondpads. The FOS over design results in a thin adhesive bondline between the slider and the stainless steel gimbal. Historically, this has provided consistent resistance performance required by the drive design. The HGA automation process requires a FOS under configuration, or FOS on the disk side of the suspension. This FOS under configuration implements a slider to FOS trace ballbond interconnect process. This new configuration employs a layer of polyimide spaced between the slider and stainless steel gimbal. The increased slider to gimbal spacing increased the bondline resistance (to greater than 108 ohms) and drove the requirement for new wafer level processes to compensate for slider to FOS trace alignment tolerances. Therefore, there is a need for an HGA that provides a small bondline resistance to improve BER (bit error rate), reduce system noise, and match ESD/EOS wafer design protection feature requirements.
Typically, the slider is placed on the gimbal with respect to a load point on the load beam. The load beam has a dimple located at its distal end which serves as the load point. The gimbal is attached to the load beam such that it balances about the dimple and the flex circuit is attached to the gimbal so that the flex circuit is centered relative to the dimple. Placing the slider with respect to the dimple minimizes the degradation of the slider's fly height above the disc. However, by placing the slider on the gimbal with respect to the dimple, the slider bond pads are often either too far away or too far forward of the FOS bond pads. It results in an increased tolerance stack up of the slider with respect to the FOS bond pads.
The ball bond HGA design requires that the slider be placed in close proximity to the FOS bond pads. Furthermore, some HGA manufacturers purchase preassembled gimbals where the flex circuit material is already deposited onto the gimbal. Due to limitations in the manufacturing process, the location of the FOS bond pads may change slightly from assembly to assembly so that the precise location of the bond pads is difficult to predict. The FOS bond pad strength may be reduced as well. The unpredictability of the FOS bond pad locations make proper alignment of the slider on the gimbal more difficult, so that the likelihood of the slider bond pads aligning with the FOS bond pads decreases. As a result, the slider ends up too far away or too far forward of the FOS bond pads.
If the slider is too far away from the FOS bond pads, a too large gap occurs between the slider bond pads and the FOS bond pads. A too large gap results in a low contact area between the ball and the bond pads, therefore a weak interconnect or no connection occurs between the slider bond pad and the FOS bond pad. A weak interconnect leads to an increased potential failure mode of the electrical connection between the slider bond pads and the FOS bond pads.
If the slider is too far forward the slider overlaps the FOS bond pads. An overlapping assembly will result in a low slider-to-gimbal bond strength and a large pitch static attitude shift.
Pitch static attitude is the angle of the slider air bearing surface in relation to the baseplate of the suspension. Static attitude impacts fly height, take off velocity in the prior art system and the reliability of the head disc interface. The increased pitch of the slider due to misalignment described above results in a non planar air bearing and causes increased fly height variability. When the slider is not attached to the gimbal with the required static attitude, a post assembly adjustment must be done to change the static attitude at an additional cost and with detrimental effects to other suspension characteristics.
A slider design is needed in the art that improves the alignment between the slider and the dimple on the load beam in a manner that provides a strong interconnect between the FOS bond pads and the slider bond pads, results in a high slider to gimbal bond strength, a small pitch static attitude shift, and provides a tolerance buffer which allows the slider to be placed relative to the suspension assembly load point without degrading mechanical structure.